Helical coil resonator having movable dielectric tuning element for varying capacitance

ABSTRACT

A HELICAL COIL RESONATOR IS WOUND ON A DIELECTRIC BOBBIN HAVING A PLATFORM WITH A MOUNTING PORTION. COUPLING LOOPS ARE POSITIONED ON THE PLATFORM AND INDUCTIVELY COUPLED TO THE COIL. FOUR THREADED POSTS ON A BASE FORM A RECEPTACLE. AN OPENING IN THE BASE IS ARRANGED TO RECEIVE THE PLATFORM MOUNTING PORTION. AFTER THE COIL IS WOUND ON THE BOBBIN, AND THE COUPLING LOOPS ARE MOUNTED ON THE PLATFORM, THE BOBBIN IS MOUNTED ON THE BASE WITH THE MOUNTING PORTION POSITIONED IN THE BASE OPENING. A CUP-SHAPED DIELECTRIC TUNING ELEMENT IS THREADED IN THE RECEPTACLE FOR MOVEMENT TOWARD AND AWAY FROM THE COIL, AND A METALLIC CAN IS POSITIONED AROUND THE POSTS. THE CAPACITY BETWEEN THE COIL AND THE CAN, AND HENCE THE RESONANT FREQUENCY OF THE RESONATOR, IS VARIED BY MOVING THE TUNING ELEMENT RELATIVE TO THE COIL.

3,555,467 HELICAL COIL RESONATOR HAVING MOVABLE DIELECTRIC TUNING Jan. 12, 1971 B. K. A. JOHNSON ELEMENT FOR VARYING CAPACITANCE Filed March 19, 1969 INVENTOR BRIAN K A JOHNSON TORNEY u viva...

United States Patent O 3,555,467 HELICAL COIL RESONATOR HAVING MOVABLE DIELECTRIC TUNING ELEMENT FOR VARYIN G 'CAPACITAN CE Brian K. A. Johnson, Lynchburg, Va., assignor to General Electric Company, a corporation of New York Filed Mar. 19, 1969, Ser. No. 808,477 Int. Cl. I-I03j 3/20 US. Cl. 334-78 8 Claims ABSTRACT OF THE DISCLOSURE A helical coil resonator is wound on a dielectric bobbin having a platform with a mounting portion. Coupling loops are positioned on the platform and inductively coupled to the coil. Four threaded posts on a base form a receptacle. An opening in the base is arranged to receive the platform mounting portion. After the coil is Wound on the bobbin, and the coupling loops are mounted on the platform, the bobbin is mounted on the base with H the mounting portion positioned in the base opening. A cup-shaped dielectric tuning element is threaded in the receptacle for movement toward and away from the coil, and a metallic can is positioned around the posts. The capacity between the coil and the can, and hence the resonant frequency of the resonator, is varied by moving the tuning element relative to the coil.

BACKGROUND OF INVENTION My invention relates to an improved coil construction, and articularly to an improved coil, construction with coupling loops that is easy to manufacture.

Coils, particularly helical coils used for resonators, find many applications in radio apparatus. Such coils represent a considerable portion of the cost of radio apparatus, and hence ways are constantly being sought to make such coils as inexpensive as possible. This is particularly true as the frequency of the radio apparatus increases, since an increased frequency usually requires a. physically smaller coil. A physically smaller coil requires more precise and hence more expensive manufacturing techniques, particularly where a coupling must be provided in order to couple the coil to an external circuit.

Accordingly, an object of my invention is to provide a new and improved coil construction for radio frequency apparatus.

Another object of my invention is to provide an improved coil and coupling loop that are relatively easy to manufacture, and hence relatively inexpensive.

Another object of my invention is to provide a new and improved coil construction having one or more coupling loops arranged in a compact, strong, but relatively easily made structure.

Another object of my invention is to provide an improved coil and coupling loop construction that provides accurately controlled coupling between the coil and coupling loop, even though the coil and coupling loops are relatively small.

SUMMARY OF THE INVENTION Briefly, these and other objects are achieved in accordance with our invention by a coil bobbin made of dielectric material, and preferably having grooves. A platform is positioned at one end of the bobbin, and a mounting portion of selected configuration is positioned beneath the platform. A coil is wound about the bobbin, and one or more coupling loops are mounted on the platform. After-the coil and coupling loops are attached, the bobbin is mounted on a base having an opening that mates with the mounting portion. The base has four posts which ex- "ice tend upward from the base and which have threaded surfaces on their inner faces to provide a threaded receptacle. A dielectric tuning element, preferably cupshaped, is provided with external threads for fitting in the threaded receptacle. A metallic element, preferably in the form of a can, is positioned around the posts and connected to one end of the coil. As the tuning element is moved toward or away from the coil by rotation, the amount of dielectric material between the coil and metallic element is varied, so that the capacitance associated with the coil is also varied. This variable capacitance can be used to adjust the resonant frequency of the coil to a desired value. Thus, my construction provides a coil and coupling loops which can be easily manufactured and tuned.

BRIEF DESCRIPTION OF THE DRAWING The subject matter which I regard as my invention is particularly pointed out and distinctly claimed in the claims. The structure and operation of my invention, together with further objects and advantages, may be better understood from the following description given in connection with the accompanying drawing, in which:

FIG. 1 shows an exploded perspective view of a coil construction in accordance with one embodiment of my invention; and

FIG. 2 shows a longitudinal cross-sectional view of my coil construction taken along a plane passing through diagonally opposite posts.

DESCRIPTION OF THE PREFERRED EMBODIMENT The embodiment of my coil construction shown in FIGS. 1 and 2 comprises a square base 10 having four posts 11a, 11b, 11c, 11d extending in a generally parallel direction upward from the base 10. I prefer four posts positioned at the corners of a square, since the posts provide good support and a compact arrangement from a space-utilization standpoint. The posts 11a, 11b, 11c, 11d are preferably formed integrally with the base 10 from a suitable dielectric material, such as polyphenylene oxide. The inner faces of the posts 11a, 11b, 11c, 11d are provided with threads 13 arranged on a common helix to form a threaded receptacle. In order that the threaded receptacle can hold an element (to be described) against vibration, the posts 11a, 11b, 11c, 11d or the threads 13 may converge inward at a slight angle. The base 10 is provided with a central hole or opening 14 for receiving the mounting portion of a coil bobbin, and with holes at the sides or corners for leads or wires to pass through the base 10.

A coil bobbin 17 is provided with a generally cylindrical shape and a helical groove 18 extending along most of the bobbin length. A platform 19 is positioned at the lower end of the bobbin 17, and as shown in FIG. 2, a locating or mounting portion 20 is positioned beneath the platform 19. The mounting portion 20 is shaped to mate or conform with and fit snugly in the hole 14 in the base 10. The bobbin 17, the platform 19, and the mounting portion 20 are preferably integrally made of a suitable dielectric material, such as the polyphenylene oxide used for the base 10. A slot 21 is formed in the platform 19, and diametrical slots 23 are formed in the upper end of the bobbin 17. When a coil is wound on the bobbin 17, an end 25a of the length of wire 25 is placed in the slot 21, and the wire 25 wound on an appropriate number of the bobbin grooves 18. The other end 25b of the wire 25 is then passed through one of the upper slots 23 and cut off so that the wound coil is securely held on the bobbin 17. One or more coupling loops 27 are mounted on the platform 19 against a suitable shoulder or projection 28 (seen in FIG. 2) on the upper face of the platform 19.

The ends 27a of the coupling loops 27 are passed through suitable holes through the platform 19 sothat the coupling loops are securely held in position on the platform 19 in the proper concentric relation with the coil formed by the wire 25. After the coil is wound on the bobbin 17 and the coupling loops 27 are mounted on the bobbin platform 19, the assembled structure is inserted between the posts 11a, 11b, 11c, 11d, so that the mounting portion 20 fits in the hole 14 in the base 10. As shown in FIG. 1, the hole 14 (and hence the mounting portion 20) may have a shape or configuration to prevent the completed structure from turning relative to the base 10. In addition, the completed structure may be cemented to the base by any suitable material, such as epoxy resin.

A tuning element 30 is provided of suitable dielectric material, such as polyphenylene oxide used for the other parts. The tuning element 30 is cylindrical in shape, and is preferably open at the bottom or cup-shaped, as shown in FIG. 2. The tuning element 30 is provided with external threads 31 of a size and pitch to fit the threads 13 provided on the inner faces of the posts 11a, 11b, 11c, 11d. If the posts 11a, 11b, 11c, 11d, or threads 13 are tapered inward at a slight angle as mentioned, the tuning element 30 will be tightly held so that vibration or shock will not change the position of the tuning element 30. High viscosity material may be placed between the threads 13, 31 to increase this holding. The tuning element 30 may also be provided with a slotted cap 32 on its upper surface so that it can be rotated by a screwdriver or other similar tool. I prefer that the tuning element 30 be cup-shaped to permit it to be moved over the coil bobbin 17, and thus provide a good range to capacitance change.

A conductive element or can 35 is positioned around the posts 11a, 11b, 11c, 11d to protect the coil construction and to provide a voltage reference point against which the coil can be tuned. The can 35 is preferably a square structure made of suitable metal, such as copper, having four sides and a top as shown. The can 35 may also be provided with a plurality of tabs 36 for holding the can 35 on the base 10, or for holding the construction on a base board.

When a coil is constructed in accordance with my invention, the coil is first wound on the bobbin 17, and the coupling loops 27 are then mounted on the platform 19. The end 25a of the coil is brought out beneath the bottom of the bobbin mounting portion 20, and the ends 27a of the coupling loops 27 are brought out through the bottom of the platform 19. The assembled bobbin, with its coil and coupling loops, is then inserted between the posts 11a, 11b, 11c, 11d, so that the mounting portion fits in the hole 14 in the base 10. The end a passes through the hole 14, and the ends 27a pass through the holes 15 in the base 10 so that external connections may be made. The completed structure may then be cemented if desired, after which the can is placed over or around the posts 11a, 11b, 11c, 11a. The tabs 36 may be bent down against the outer, lower surface of the base 10 to hold the can 35 in position (as shown); or the tabs 36 may be left straight and soldered to a base board, such as a printed circuit board. The lower end 25a of the coil wire 25 may then be soldered or fastened to one of the tabs 36 of the can 35, or to the base board. The top of the can 35 is provided with a suitable hole or opening 37 to permit a tool to be inserted within the can 35 into the slotted cap 32 for adjusting the tuning element 30.

In one embodiment of my coil construction that has actually been built and used, the coil was intended to be used at a frequency of 450 megacycles. The can 35 had a square cross section measuring .535 by .535 inch, and was .810 inch high. The coil bobbin 17 had a length of .480 inch, and a diameter of .300 inch. The bobbin 17 was wound with 6 /2 turns to provide a coil having an unloaded Q of 420 at a frequency of 450 megahertz.

This coil could be tuned between 438 and 482 megahertz, with approximately .250 inch travel of the tuning element 30. This construction was easily made and adjusted, despite its, relatively small size, because of the novel construction and arrangement of my invention. Thus, my invention provides a new and improved coil construction which makes such coils relatively easy to manufacture and adjust or tune.

While I have shown only one embodiment of my invention, persons skilled in the art will appreciate that modifications may be made. For example, the coil bobbin 17 may have various types of slots or notches to receive and hold the ends of the wire forming the coil. The tuning element 30 may have other shapes, although I prefer the cup-shaped element shown. One or more coupling loops may be provided, depending upon the application for the coil construction. Also, various platform configurations may be provided to receive the coupling loop 27, although I prefer the shoulders 28 shown in order to concentrically position the coupling loop 27 on the platform 19. Therefore, while my invention has been described with reference to a particular embodiment, it is to be understood that modifications may be made without departing from the spirit of my invention or from the scope of the claim.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. An improved coil construction for radio frequency apparatus comprising:

(a) an elongated coil bobbin formed of dielectric material for receiving a coil;

(b) a platform attached to one end of said coil bobbin, said platform having a mounting portion with a selected configuration;

(c) a coil wound about at least a portion of said bobbin to provide a selected inductance;

(d) a first coupling loop positioned on said platform and inductively coupled to said coil;

(e) a base formed of dielectric material and having an opening of said selected configuration to receive said platform mounting portion;

(f) at least three posts of dielectric material positioned on said 'base, said posts extending upwardly from said base in a substantially parallel direction, and each of said posts being threaded on an inner face thereof to provide a threaded receptacle;

(g) means mounting said platform on said base with said platform mounting portion in said base opening so that said coil and said coil bobbin extend inwardly of and along said posts;

(h) a tuning element of dielectric material having external threads arranged to fit said threaded receptacle formed by said posts, said tuning element being rotatable in said threaded receptacle to move toward and away from said coil to vary the electrical characteristics thereof;

(i) a conductive element positioned adjacent said posts;

(j) and means for connecting said coil and said coupling loop to external circuits.

2. The improved coil construction of claim 1 and comprising a second coupling p positioned on said platform and inductively coupled to said coil, said first and second coupling loops serving as input and output loops respectively.

3. The improved coil construction of claim 2 wherein said coil bobbin has a substantially cylindrical shape, and wherein said first and second coupling loops are concentrically positioned relative to said coil bobbin.

4. The improved coil construction of claim 1, and comprising four substantially similar dielectric posts respectively positioned at the four corners of a square on said base, said posts extending upwardly from said base in a direction generally parallel to each other, and said posts being threaded on an inner face to provide a threaded -receptacle, and said conductive element comprising a can positioned around said posts.

5. The improved coil construction of claim 4 and comprising a second coupling loop positioned on said platform and inductively coupled to said coil, said first and second coupling loops serving as input and output loops respectively.

6. The improved coil construction of claim 5 wherein said coil bobbin has a substantially cylindrical shape, and wherein said first and second coupling loops are concentrically positioned relative to said coil bobbin.

7. The improved coil construction of claim 6 wherein said tuning element is cup-shaped for fitting partially around said coil bobbin.

References Cited UNITED STATES PATENTS 4/1966 Buctow et a]. 33482X 2/1967 Loos 334-82X 10 PAUL L. GENSLER, Primary Examiner U.S. Cl. X.R. 

